Citing rocketing achievement numbers, charter-school backers are demanding that Mayor de Blasio establish an additional 200,000 seats for the expanding sector across New York City.

Families for Excellent Schools claims that the proposed growth — which would roughly double the sector’s size — would help to eliminate chronic achievement deficits between low-income students and their peers.

“Doubling the city’s charter sector to 200,000 children would eliminate the achievement gap in the city’s poorest neighborhoods,” said Jeremiah Kittredge, CEO of FES. “If city leaders are serious about ending education inequality, then they must double the size of the city’s charter sector.”

FES said that charter school kids in the city’s eight worst performing public school districts have a 146 percent better shot at math and English proficiency.

The advocacy group noted that a recent report counted roughly 150,000 unused classroom seats in public schools that could be used to accommodate charter school students.

The group is planning a march at Prospect Park in Brooklyn later this month to pressure de Blasio into increasing their reach, in order to ease massive wait lists.

De Blasio recently poured cold water on charter school achievements, arguing they put inordinate emphasis on test scores .